1. Field of the Invention
The present invention relates to a method for detecting misfire in an automobile engine, and more particularly to an automobile engine misfire detecting method using a response signal from a widexe2x80x94range oxygen sensor to detect misfiring in an automobile engine.
2. Description of the Prior Art
According to the conventional detecting and judging method of engine misfire, as illustrated in FIGS. 1 and 2, an Electronic Control Unit (ECU) receives information on engine load, engine Revolutions Per Minute (RPM), cooling water temperature, and receives signals from a crank angle sensor, a phase sensor and a widexe2x80x94range oxygen sensor mounted on a junction point of the exhaust manifold, where the signals from the wide-band oxygen sensor are sampled based on crank angle under a predetermined operational condition to calculate a fluctuated incline curve, and when the incline of the signal surpasses a standard value under a predetermined engine load and engine RPM, it is determined that a misfire has occurred in the engine.
At the same time, a phase difference is calculated between a second peak position of a fluctuated incline curve of the signal from the widexe2x80x94range oxygen sensor and signal from the phase sensor to compare the same with a standard phase angle range, by which a judgment is made on from which cylinder the misfire has occurred to enable lighting of a warning light of xe2x80x9cCheck Enginexe2x80x9d.
In other words, when a misfire occurs, a large quantity of oxygen is generated from the exhaust gas and a sudden change of oxygen concentration is detected by a widexe2x80x94range oxygen sensor, by which it is judged that a misfire has occurred when the fluctuated incline curve of the signal from the widexe2x80x94range oxygen sensor for showing changes of oxygen concentration in a predetermined engine load and engine RPM surpasses a standard value. The reason of using the fluctuated incline curve of the signal instead of signal itself from the widexe2x80x94range oxygen sensor is that, even in a normal burnt state, the signal (voltage) from the widexe2x80x94range oxygen sensor is increased when driving is performed in a low air fuel ratio, such that distinction should be made therefrom.
Next, the following principle is applied to judge from which cylinder a misfire has occurred.
When a misfire is generated in a cylinder, misfired exhaust gas is discharged via an exhaust manifold to enable detecting of changes of oxygen concentration by way of the widexe2x80x94range oxygen sensor.
In case misfire occurs in the nth time, the abrupt change of oxygen concentration detected by the widexe2x80x94range oxygen sensor is detected in the n+1 time, which is a general phenomenon where the misfired exhaust gas is not discharged from the exhaust manifold at one time only to be mixed with other exhaust gases discharged from other cylinders.
FIG. 3 illustrates the nth time of misfire relative to the n+1 time of oxygen concentration change, where, when misfire occurs one time at crank angle of approximately 300xcx9c500 degrees, it can be noted that sudden changes (Peaks) of oxygen concentration are detected respectively at approximately 900 degrees and 1,300 degrees of crank angle.
In a generalized form, when the nth time of continuous misfire occurs at one cylinder, n+1 time of peaks occur over n+1 cycle, and when the continuous misfires occur at two cylinders, it can be noted that peaks of 2n+1 time occur over n+1 cycle, where 1 cycle is 720 degrees which is two times the revolution of crank shaft where one cylinder completes four strokes.
In order to judge a misfired cylinder by using the afore said principle, a signal which is the base for discriminating each cycle is necessary, and signals from phase sensor are used therefore. The phase sensor is a sensor for providing pulses at each revolution of a cam shaft, or providing pulses dropping to zero voltage at every 720 degrees as shown in FIG. 3.
A misfired cylinder is judged from a relation between a standard pulse of phase sensor thus provided and peak of the fluctuated incline curve of the signal detected by the widexe2x80x94range oxygen sensor. A phase difference is calculated up to the second peak of fluctuated incline curve of the signal of oxygen concentration caused by misfire from a standard pulse of the phase sensor to discriminate a misfired cylinder according to which range of the standard phase angle the relevant phase difference belongs.
In other words, if a phase difference thus calculated is within xcex81 (engine revolution N, engine load L)xcx9cxcex82 (N, L), it is judged that a misfire has occurred at the first, cylinder.
If the phase difference is in the range of xcex82 (N, L)xcx9cxcex83 (N, L), it is judged that a misfire has occurred at the third cylinder. If within xcex83 (N, L)xcx9cxcex84 (N, L), a misfire is presumed to have occurred at the fourth cylinder, and if within xcex84 (N, L)xcx9cxcex81 (N, L)+720 degrees, it is discriminated that a misfire has occurred at the second cylinder.
Detection of these kinds of misfire occurrence and judgment of misfired cylinders can be explained from the flow chart of FIG. 4, which includes the steps of receiving signals from various sensors to discriminate whether a fluctuated incline curve of the signal from widexe2x80x94range oxygen sensor surpasses the standard value, calculating a phase difference of a second peak at the fluctuated incline signal from the widexe2x80x94range oxygen sensor relative to a standard pulse of phase sensor and judging to which standard phase angle range the calculated phase difference belongs, to thereby discriminate a cylinder on which a misfire has occurred.
However, there is a problem in the judging method of engine misfire and misfired cylinder by way of a signal detected from the widexe2x80x94range oxygen sensor thus described in that misfire detection efficiency and judging efficiency of misfired cylinder deteriorates according to an over response characteristic change of the widexe2x80x94range oxygen sensor.
Particularly, there is a problem in that the response characteristic of sensor slows down as the sensor becomes aged to decrease a fluctuated width of the sensor signal, and the phase difference between phase sensor signal used for distinguishing the misfired cylinder and a position of second peak at the fluctuated incline curve of the signal from the widexe2x80x94range oxygen sensor is also changed to markedly decrease misfire occurrence and misfired cylinder distinguishing probability.
There is still another problem in that a response characteristic relative to misfired gas of widexe2x80x94range oxygen sensor used for misfire detection varies per sensor, resulting in the changes in misfire detection performance per sensor.
The present invention solves the aforementioned problems and provides an automobile engine misfire detecting method which measures a response characteristic of a widexe2x80x94range oxygen sensor relative to sudden concentration changes of oxygen prior to entry of conventional misfire detection judging logic on which a standard phase angle range is corrected for distinguishing a standard value of misfire detection judgment and a misfired cylinder to thereby enable judging of an accurate misfire detection and misfired cylinder.
In accordance with the present invention, there is provided an automobile engine misfire detecting method, the method comprising the steps of:
abruptly decreasing fuel injection under a predetermined engine operation condition by a predetermined amount to measure changes of signals from a widexe2x80x94range oxygen sensor before and after the fuel injection decrease;
correcting a standard value for judging misfire according to changes of signals from a widexe2x80x94range oxygen sensor measured at the sensor characteristic measurement step;
judging that a misfire has occurred if it is discriminated that a fluctuated incline curve of the signal from the widexe2x80x94range oxygen sensor has surpassed the corrected standard value;
calculating a phase difference between a standard pulse of phase sensor and a second peak at the fluctuated incline curve of the signal from the widexe2x80x94range oxygen sensor at the time of the misfire occurrence; and
judging which corrected standard phase angle range the calculated phase difference belongs to to discriminate a cylinder where a misfire has occurred.